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Glossary

Glossary

AAC (Advanced Audio Coding) Also called MPEG-4 Audio. A standard way of compressing and encoding digital audio. AAC-encoded files rival the quality of audio CDs and generally sound as good as or better than MP3 files encoded at the same or even a higher bit rate.

AIFF (Audio Interchange File Format) A cross-platform audio file format developed by Apple. Like WAV files, AIFF files contain “chunks” of information such as the Sound Data Chunk, which contains the actual sample data, and the Common Chunk, which contains sample rate and bit depth information.

Apple ProRes 4444 XQ: The highest-quality version of Apple ProRes for 4:4:4:4 image sources (including alpha channels), with a very high data rate to preserve the detail in high-dynamic-range imagery generated by today’s highest-quality digital image sensors. Apple ProRes 4444 XQ preserves dynamic ranges several times greater than the dynamic range of Rec 709 imagery—even against the rigors of extreme visual effects processing, in which tone-scale blacks or highlights are stretched significantly. Like standard Apple ProRes 4444, this codec supports up to 12 bits per image channel and up to 16 bits for the alpha channel. Apple ProRes 4444 XQ features a target data rate of approximately 500 Mbps for 4:4:4 sources at 1920 x 1080 and 29.97 fps.

Apple ProRes 4444: An extremely high-quality version of Apple ProRes for 4:4:4:4 image sources (including alpha channels). This codec features full-resolution, mastering-quality 4:4:4:4 RGBA color and visual fidelity that is perceptually indistinguishable from the original material. Apple ProRes 4444 is a high-quality solution for storing and exchanging motion graphics and composites, with excellent multigeneration performance and a mathematically lossless alpha channel up to 16 bits. This codec features a remarkably low data rate compared to uncompressed 4:4:4 HD, with a target data rate of approximately 330 Mbps for 4:4:4 sources at 1920 x 1080 and 29.97 fps. It also offers direct encoding of, and decoding to, both RGB and Y’CBCR pixel formats.

Apple ProRes 422 HQ: A higher-data-rate version of Apple ProRes 422 that preserves visual quality at the same high level as Apple ProRes 4444, but for 4:2:2 image sources. With widespread adoption across the video post-production industry, Apple ProRes 422 HQ offers visually lossless preservation of the highest-quality professional HD video that a single-link HD-SDI signal can carry. This codec supports full-width, 4:2:2 video sources at 10-bit pixel depths, while remaining visually lossless through many generations of decoding and reencoding. The target data rate of Apple ProRes 422 HQ is approximately 220 Mbps at 1920 x 1080 and 29.97 fps.

Apple ProRes 422: A high-quality compressed codec offering nearly all the benefits of Apple ProRes 422 HQ, but at 66 percent of the data rate for even better multistream, real-time editing performance. The target data rate of Apple ProRes 422 is approximately 147 Mbps at 1920 x 1080 and 29.97 fps.

Apple ProRes 422 LT: A more highly compressed codec than Apple ProRes 422, with roughly 70 percent of the data rate and 30 percent smaller file sizes. This codec is perfect for environments where storage capacity and data rate are at a premium. The target data rate of Apple ProRes 422 LT is approximately 102 Mbps at 1920 x 1080 and 29.97 fps.

Apple ProRes 422 Proxy: An even more highly compressed codec than Apple ProRes 422 LT, intended for use in offline workflows that require low data rates but full-resolution video. The target data rate of Apple ProRes 422 Proxy is approximately 45 Mbps at 1920 x 1080 and 29.97 fps.

Note: Apple ProRes 4444 and Apple ProRes 4444 XQ are ideal for the exchange of motion graphics media because they are virtually lossless, and are the only Apple ProRes codecs that support alpha channels.

AVCHD A high-definition (HD) video format that uses Advanced Video Coding (AVC) compression (also known as MPEG-4 part 10 or H.264). Many Blu-ray players can play red laser discs with AVCHD format content, making this a common way to distribute short HD video projects using a standard red laser disc.

Batch In Compressor, one or more jobs to be processed. All jobs contained within the batch (shown in the batch area of Compressor window) are submitted collectively when you begin the transcoding process.

Bit rate The number of bits per second in the transmission of a digital video or audio signal. The higher you set the bit rate, the better the quality of the output file. However, higher bit rates require larger file sizes.

Closed captions Onscreen text corresponding to the audio of a video program. Originally developed for hearing-impaired viewers, closed captioning (also known as line 21 text) is also frequently used on televisions in loud environments (such as restaurants and bars) or in locations where playing the audio might be considered rude or inappropriate (such as hospital waiting rooms).

Codec Short for COmpression/DECompression. A software component used to translate video or audio from its current form to a different, digitally compressed form. A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. A similar term, encoder, is used to describe hardware that performs the same activity.

Delivery partner A content aggregator or encoding house certified by the iTunes Store and authorized to submit iTunes Store packages to the store for sale. These partners ensure your content is properly configured and formatted to meet the stringent submission requirements of the iTunes Store. They can also provide billing and support services after your video becomes available for sale.

Destination In Compressor, a group of one or more transcode settings plus a post-transcoding action. If you use a destination to transcode a file, one or more new files are created to the setting’s specifications, and then an action is automatically performed on the transcoded file. For example, the Publish to Facebook destination outputs the source file using the HD 720p QuickTime setting, creating a file optimized for viewing on the web and on mobile devices such as iPad and iPhone. After the file is processed, the Publishing to Facebook action automatically posts the output file to your Facebook account.

Display aspect ratio The ratio between an image’s width and height. For example, Standard-definition (SD) video typically has an aspect ratio of 4:3. High-definition (HD) video typically has an aspect ratio of 16:9. If SD video is played on an HD display, the image is either stretched or appended with black borders on left and right sides (pillarboxes). If HD video is played on an SD display, the image will be squeezed or black borders will appear at the top and bottom (letterboxes).

Distributed processing A method of transcoding that accelerates processing of Compressor batches by distributing the work among multiple computer processors. A system can distribute parts of a batch to multiple instances of the Compressor application on a single computer, or to two or more networked computers (each running one or more instances of Compressor).

Encoder See codec.

File format The output format used to transcode your source media file. Also called a transcoding format.

H.264 A video compression standard in widespread use for recording, distribution, and Internet streaming of high-definition (HD) video. Also known as MPEG-4 Part 10 or AVC (Advanced Video Coding).

I-Frame (intra-coded picture) One type of frame used to define the GOP (Group of Pictures) pattern used during MPEG-2 or H.264 encoding. A GOP pattern can also include P-frames (predictive coded picture) and B-frames (bipredicitive coded picture)

Interlaced video Video to be played on traditional NTSC or PAL televisions is stored using an interlaced frame rate. Each frame is actually made up of two half-frames called fields. Each field contains half the frame lines; the odd (or upper) field contains lines 1, 3, 5, 7, 9 and so on, and the even (or lower) field contains lines 2, 4, 6, 8, 10, and so on. When the video is played back, the TV displays the fields in an alternating pattern, which creates an effective illusion of smooth movement. Viewing interlaced video on a computer screen that displays both fields simultaneously may reveal a combing effect. Progressive video frame rates store the video in a series of whole frames instead these two-fields. You can remove the fields from an interlaced video clip by converting it to a progressive frame rate.

iTunes Store Package Publishers who submit videos to the iTunes Store must deliver their content in a carefully prescribed format called an iTunes Store package. Compressor can create these packages, provided you have all the requisite components (video files, audio files, subtitle files, closed-caption files, and so on).

iTT subtitle format The iTT (iTunes timed text) file format is a subset of the Timed Text Markup Language, Version 1.0 W3C Candidate Recommendation 23 February 2010 (TTML) from the World Wide Web Consortium (W3C). All iTT documents are TTML documents that use a restricted subset of TTML. In addition to providing text and timing, an iTT document specifies the font style, font color, text alignment, and layout of the timed text.

Job In Compressor, the source media file and output instructions (one or more output rows, each containing a setting, location, and file name), ready to be transcoded.

Job action In Compressor, an action that is performed on a media file after it is transcoded. For example, a job action can add a transcoded file to iTunes or publish a transcoded file to a popular video-sharing website like YouTube.

Key frame interval A key frame is a frame that stores a complete image. Key frames provide the entire image in the video stream; after that image is provided, incremental changes between related frames are stored (not the entire image). Thus, when the image in the video changes dramatically, for example, when switching between images, a keyframe must be created to mark the location of change. It’s recommended that you allow Compressor to determine the key frame interval for your output file; however, you can also set the key frame interval manually.

Location In Compressor, the location where your transcoded media file is saved. You can either use the default location (the same folder the source media file is in) or choose a custom location.

Lower third A television industry term for a graphic placed in the lower area of the screen, usually to convey details about subjects or products. A common use of lower thirds is to identify individuals on the screen with their names and job titles.

Markers A marker flags a specific timing location in a source file. You can append a marker with editing notes or other descriptive information. Additionally, when you output the source file to an H.264, MPEG-2, or MPEG-4 video format, each marker forces the creation of an I-frame. Added I-frames improve compression quality, but can increase overall file size. Compressor can create the following types of markers:

Chapter markers: Generate named index points and thumbnail images for DVDs, QuickTime movies, or video podcasts. You can also assign a URL to a chapter marker to have that URL appear during playback of a podcast. Chapter markers are also included in submissions to the iTunes Store as part of an iTunes Store Package. Chapter markers appear orange in the Compressor preview area.

Compression markers: Generate an I-frame, but do not generate thumbnails, chapter-track entries, or other metadata. Add them to a video if a section appears to have lower image quality than the surrounding frames. Compression markers appear blue in the Compressor preview area.

Edit/cut markers: Function identically to Compression markers. They are commonly used by compression artists to force an I-frame at an edit point to ensure higher image quality at that moment in the video. Edit/cut markers appear red in the Compressor preview area.

Podcast markers: Like chapter markers, Podcast markers can have artwork and a URL assigned to them. Podcast markers are usually used to provide a slideshow (with URLs) for users to view when playing audio podcasts. However, podcast marker names do not appear in the slideshow, and users cannot navigate to a podcast marker in the transcoded file. Podcast markers appear purple in the Compressor preview area.

Matrix stereo A stereo downmix of a surround track for playback on a device with only two speakers; matrix stereo can also be decoded to play the full surround mix on a surround-capable playback device.

Output row In Compressor, an output row in a job contains the instructions used for transcoding a source media file. An output row includes a setting (shown on the left) that specifies properties defining how to transcode the source media file, a location (shown in the middle) where the transcoded file will be saved, and a filename (shown on the right) for the transcoded file.

QuickTime The cross-platform multimedia technology that allows OS X and Windows applications to capture and play back video, audio, and still-image files.

Preview area In Compressor, the area where you can play your source file and preview your output file. After you apply effects or change the properties of the setting that will transcode your source file, you can compare the “before” and “after” versions by clicking the Comparison button (under the timeline). The screen is divided by a vertical white line, with the source file shown on the left and the preview of the transcoded file shown on the right.

Resolution Image resolution refers to the frame size of the video. Image resolution is expressed in terms of the width and height (the frame size) of the image in pixels. Higher-resolution images contain more detail but also create larger files that take longer to download. Your electronic devices (computer, iPhone, iPad, iPod, and so on) also have screen resolution. Resolution is expressed in terms of the width and height of the image in pixels (for example, 640 x 360 pixels).

When you add a setting to a source media file, Compressor determines appropriate resolution sizes you can use, based on the image sizes used in the movie and on the setting that you’re using to output the file.

Sample rate The number of times per second that music waveforms (samples) are captured digitally. The higher the sample rate, the higher the quality and the larger the file size.

Sample size The number of bits in each audio sample; determines the potential dynamic range of the sound.

Setting In Compressor, a group of properties that are used to transcode a source media file. Each setting contains the following properties (which you can modify in the Inspector pane):

Frame size, pixel aspect ratio, and cropping and padding controls that allow you to crop the image and adjust its frame size.

Video and audio effects that modify different characteristics of your video or audio to maximize the quality of the output file.

Storage aspect ratio (SAR) The ratio between an image’s width and height when it is stored. Storage aspect ratio can differ from display aspect ratio (DAR) resulting in a file that must be stretched or squeezed during playback to appear correct. This disparity can allow a camera format limited to 4:3 recording to successfully record a widescreen image by “squeezing” the image during recording. If the image is unsqueezed during playback it will display correctly in its widescreen aspect ratio. This is called an anamorphic image.

Source media file In Compressor, the original media file to be converted to a new file format. One source file is required for each job.

Transcoding The process of converting files from their original format to a different format. Closely related terms include compression, which specifically refers to data reduction, and encoding, a term that is essentially synonymous with transcoding, but doesn’t emphasize the conversion aspect.

Uncompressed 8-bit and 10-bit 4:2:2 Video formats used to store 8-bit or 10-bit 4:2:2 Y’CBCR video without employing data compression. Bypassing compression reduces the computer’s processing load but increases the data rate considerably. A large-capacity RAID storage system is typically required to work effectively with uncompressed video. In many cases, Apple ProRes is a better choice.

The data rate of uncompressed 4:2:2 video varies according to frame size and frame rate. For example, at a frame size of 1920 x 1080 and a frame rate of 29.97 fps, the data rate is 1.0 Gbps for uncompressed 8-bit 4:2:2 video and 1.3 Gbps for uncompressed 10-bit 4:2:2 video.